Washington state hot spot for toll projects - 99 Tunnel under downtown Seattle

Washington state is a hot spot for new toll projects - and big, bold projects to boot. We reported recently on the array of alternatives being considered for the longrange transportation plan for the region - all of which involve substantial reliance on tolls - plus acceptance of tolls on the presently untolled 520 bridge ahead of construction of a wider replacement bridge, but there's more.

- toll studies are underway for I-405/WA167 the major north-south route, much of planned as 2x2 HOT lanes for a total of 290 lane-km (180 lane-miles)

- toll studies for reconstruction of bridges over the Columbia River between Washington and Oregon at I-5 and I-205 15km (9 miles) upstream

99 Tunnel

The biggest new road tunnel in America - through downtown Seattle - seems to be moving ahead with wide support as a toll facility. The 99 Tunnel we'll call it, will be the world's first bored tunnel to carry full height trucks and buses in 2x2 lanes providing for overhead clearance of 5.03m (16.5ft) and breakdown shoulders in an efficient doubledeck configuration. Construction will use a tunnel boring machine (TBM) that bores an external tube of 16.45m (54ft) diameter, the largest yet for a road - though apparently the Gotthard Base Tunnel for freight rail under the Alps is being built with a 19m (62.3ft) TBM.

Full height trucks must be able to use Washington state route 99 (WA99) because there are port and warehousing areas along the road. Construction of the 99 Tunnel will allow the demolition of the old Alaskan Way Viaduct, (WA99), rebuilding of the seawall nearby and improvements to local streets and streetscapes. The Viaduct is a 1950s mostly doubledeck elevated of reinforced concrete, damaged in the last earthquake, an eyesore, and at the end its useful life.

The 99 Tunnel has been initially costed at $944m, but Washington DOT have added to their estimates design and construction management $236m and right of way at $149m for a total of $1.33b (at 7.5 lane miles that's$173m/lane-mile, $108m/lane-km), but they quote $1.91b including "escalation" (inflation) and a big "risk factor" (political hazard?).  That's $255m/lane-mile, $158m/lane-km. Hatch Mott MacDonald the international engineering firm is providing in-house advice on engineering aspects of the procurement.  The legislature in a  bill passed some months ago (SB5768) which initially required that the project support toll revenue of "at least $400m." But the final bill as signed by the Governor states that tolling must generate "up to $400m."

A less-than-investment-grade traffic and revenue study is being conducted on the 99 Tunnel by Parsons Brinckerhoff to establish how much the toll potential of the tunnel. It has to be submitted to the legislature early next year.

Traffic on the untolled 2x3 lane elevated averages 110k/day. Under the plan the six 1950s expressway lanes of the elevated will be replaced by:

(1) 4 modern expressway lanes underground (the 99 Tunnel) and

(2) 4 signalized arterial surface lanes in a boulevard type configuration

BACK O' ENVELOPE 'RITHMETICK: Depending on the time advantage and toll rates the 99 Tunnel should get at least half the traffic of the viaduct or 60k/day. If time savings are the difference between 60mph (100km/hr) in the tunnel and 15mph (25km/hr) average on the surface boulevard then time savings would be 2mins v 8mins or 6mins. At $30/hr vehicle time savings using the tunnel vs the surface boulevard would be $3.00. If the toll is set at the average value of time savings $3x60k=$180k/day = $66m/yr.

If operating costs were 15% there'd be a $50m revenue stream.

Capital/cash flow revenues ratios of 40/1 ($2b) have been paid in the past for tollroads with established traffic but assuming a more sober ratio of say 12/1 you get $600m - over the legislature's requirement but not sufficient to make the tunnel a self-financer.

On this arithmetic above a 20/1 ratio, (half the ratios on the Chicago Skyway and Indiana Toll Road concessions,) would the 99 Tunnel be close to financial viability as a standalone toll financed project.

Dimensions

The new 99 Tunnel will be somewhere between 2.8km and 3.4km (1.75mi and 2.1 miles) long depending on final locations of the portals. It will accomodate a double deck of about 10.7m (35ft) width for twin 3.66m (12ft) travel lanes plus a full 3.05m (10ft) shoulder plus an offset on each level.

The tunnel can't have any intermediate ventilation tower so the segments left from fitting two rectangular road segments in to the circular shape are used for air (and utilities.)

World's biggest borer for first doubledecker for full height vehicles

Previously it has been normal for bored tunnels to have a separate tube for each direction of traffic. There are obviously major economies in a single tube.

So far as we know the world's first bored doubledecker highway tunnel to open will be the 10km-long (6.2 miles) A86W west of Paris, a Cofiroute project with a ceiling at 2.55m (8ft4 inches) providing for 2m (6ft7in) cars-only clearance, the difference being overhead space for signs.

This Paris tunnel is built with a TBM 10.4m (34.1ft) diameter, under two-thirds the 16.45m (54ft) diameter of the proposed machine for Seattle.

video see on Paris tunnel:

 http://www.youtube.com/watch?v=MXgth_yrNIg

In Shanghai China, Herrenknecht of Germany, the world's leading maker of large tunnel boring machines recently opened twin tunnels under the Yangtze River using a 15.43m (50.6ft) diameter TBM.

These tubes accommodate three roadway lanes on the top deck plus a single rail subway line under the road deck in each tube. 

The 7.5km (4.6 mile) long Shanghai-Changjiang Yangtze River tunnels were built on budget and ahead of schedule.

A similar three road lanes on top of a single rail line was used in twin tunnels for the M30 in Madrid Spain that opened in 2004. The M30 tunnels used a 15.20m (49.9ft) boring machine.

TBM's seem less risky

On average more expensive than the New Austrian method using less elaborate roadheader machines and different stabilization methods according to the immediate geology, the tunnel boring machine method seems less risky, especially for longer deeper tunnels.

Because of the many entries and exits Boston's Big Dig had to be a very shallow tunnel, and was constructed by cut-&-cover methods.

video on TBMs:

http://www.youtube.com/watch?v=yFHrI3HFMDg

TOLLROADSnews 2009-06-21